Multi-level mems process
An actuator layer of a MEMS sensor is be fabricated to include multi-level features, such as additional sense electrodes, vertical bump stops, or weighted proof masses. A sacrificial layer is deposited on the actuator layer such that locations are provided for the multi-level features to extend vertically from the actuator layer. After the multi-layer features are fabricated on the actuator layer the sacrificial layer is removed. Additional processing such as patterning of the actuator layer may be performed to provide desired functionality and electrical signals to portions of the actuator layer, including to the multi-level features.
1 . A method of fabricating a multi-level microelectromechanical system (MEMS) sensor, comprising:
providing an actuator layer;
applying a sacrificial layer to a first surface of the actuator layer, wherein one or more openings within the sacrificial layer correspond to one or more multi-level features;
fabricating the one or more multi-level features on the actuator layer, wherein the one or more multi-level features extend from the first surface of the actuator layer through the one or more openings in the sacrificial layer;
removing the sacrificial layer, wherein after removal of the sacrificial layer an intra-layer cavity separates a portion of the first surface of the actuator layer from the one or more multi-level features;
bonding a handle layer overlying the multi-level features to the actuator layer, wherein after the bonding of the handle layer a cavity is formed over the multi-level features; and
bonding a substrate layer to at least a portion of a second surface of the actuator layer, wherein after the bonding of the substrate layer a patterned portion of the actuator layer is suspended over the substrate layer.
2 . The method of claim 1 , further comprising patterning, after the bonding to the handle layer, the second surface of the actuator layer to create the patterned portion.
3 . The method of claim 2 , further comprising grinding the second surface of the actuator layer to a target thickness prior to the patterning.
4 . The method of claim 2 , wherein the second surface of the actuator layer is located opposite the first surface of the actuator layer.
5 . The method of claim 2 , further comprising removing an additional portion of material of the actuator layer after the patterning to electrically and mechanically isolate at least one of the one or more multi-level features from other portions of the actuator layer.
6 . The method of claim 5 , wherein the additional portion of material of the actuator is removed by deep reactive-ion etching.
7 . The method of claim 5 , wherein the substrate layer comprises a complementary metal-oxide semiconductor (CMOS) layer.
8 . The method of claim 5 , wherein an electrical signal is provided to the isolated at least one multi-level feature via the substrate layer.
9 . The method of claim 1 , wherein the handle layer comprises one or more posts that extend in a direction of the first surface of the actuator layer to bond to the first surface of the actuator layer.
10 . The method of claim 1 , wherein the sacrificial layer comprises silicon oxide.
11 . The method of claim 1 , further comprising:
applying, prior to the removal of the sacrificial layer, a dielectric mask over portions of the sacrificial layer and portions of the one or more multi-level features; and
fabricating one or more posts from the actuator layer or the one or more multi-level features, wherein a location of the one or more posts is based on one or more openings of the dielectric mask, and wherein the bonding of the handle layer to the actuator layer is via the one or more posts.
12 . The method of claim 11 , further comprising:
grinding the second surface of the actuator layer to a target thickness; and
patterning, after the bonding to the handle layer and grinding, the second surface of the actuator layer to create the patterned portion.
13 . The method of claim 12 , further comprising removing an additional portion of material of the actuator layer after the patterning to electrically and mechanically isolate at least one of the one or more multi-level features from other portions of the actuator layer.
14 . The method of claim 1 , wherein at least one of the one or more multi-level features comprises a sense electrode located between the handle layer and a portion of the first surface.
15 . The method of claim 1 , wherein at least one of the one or more multi-level features comprises a bump stop located between the handle layer and a portion of the first surface.
16 . The method of claim 1 , wherein at least one of the one or more multi-level features comprises a weighted portion located between the handle layer and a portion of the first surface.
17 . The method of claim 1 , wherein at least one of the one or more multi-level features comprises a mechanical bridge structure located between the handle layer and a portion of the first surface, and wherein the mechanical bridge structure connects at least two portions of the actuator layer.
18 . The method of claim 1 , wherein bonding the handle layer comprises bonding the handle layer to the one or more multi-level features on the actuator layer.